linux-kernel - Re: [PATCH] dmaengine: plx_dma: Fix potential deadlock on &plxdev->ring

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Date:   Wed, 26 Jul 2023 09:57:16 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Chengfeng Ye <dg573847474@...il.com>, vkoul@...nel.org
Cc:     dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: plx_dma: Fix potential deadlock on
 &plxdev->ring_lock



On 2023-07-26 04:48, Chengfeng Ye wrote:
> As plx_dma_process_desc() is invoked by both tasklet plx_dma_desc_task()
> under softirq context and plx_dma_tx_status() callback that executed under
> process context, the lock aquicision of &plxdev->ring_lock inside
> plx_dma_process_desc() should disable irq otherwise deadlock could happen
> if the irq preempts the execution of process context code while the lock
> is held in process context on the same CPU.
> 
> Possible deadlock scenario:
> plx_dma_tx_status()
>     -> plx_dma_process_desc()
>     -> spin_lock(&plxdev->ring_lock)
>         <tasklet softirq>
>         -> plx_dma_desc_task()
>         -> plx_dma_process_desc()
>         -> spin_lock(&plxdev->ring_lock) (deadlock here)
> 
> This flaw was found by an experimental static analysis tool I am developing
> for irq-related deadlock.
> 
> The tentative patch fixes the potential deadlock by spin_lock_irqsave() in
> plx_dma_process_desc() to disable irq while lock is held.
> 
> Signed-off-by: Chengfeng Ye <dg573847474@...il.com>

Makes sense. Thanks!

Reviewed-by: Logan Gunthorpe <logang@...tatee.com>

Logan